1. Field of the Invention
The present invention relates to a method for subjecting propane to a vapor-phase catalytic ammoxidation reaction to produce a corresponding unsaturated nitrile.
2. Description of the Related Art
It is conventionally known that a method for subjecting propylene to a vapor-phase catalytic ammoxidation reaction to produce a corresponding unsaturated nitrile. In recent years, attention has been directed to a method for subjecting propane instead of propylene to a vapor-phase catalytic ammoxidation reaction to produce a corresponding unsaturated nitrile.
Hitherto, in subjecting propane to a vapor-phase catalytic ammoxidation to produce a corresponding unsaturated nitrile, various techniques have been examined, for example, a technique for adding a molybdenum compound into a reactor during the reaction to maintain the yield of a target product, or a technique for again impregnation with, calcination of, and drying of a catalyst to restore the yield of a target product if the catalyst is deactivated by the reaction.
For example, Patent Literature 1 discloses a technique for adding a molybdenum compound during a vapor-phase catalytic ammoxidation reaction using a Mo—V—Sb—Nb-based catalyst.
Moreover, Patent Literature 2 describes a method for mixing a composite oxide catalyst with an additive such as an antimony compound, a molybdenum compound, a tellurium compound, and a tungsten compound, and subjecting the obtained catalyst to a reaction.
Further, Patent Literature 3 describes a method for impregnating a Mo—V—Sb/Te-based catalyst with a solution containing one or more elements selected from the group consisting of tungsten, molybdenum, chromium, zirconium, titanium, niobium, tantalum, vanadium, boron, bismuth, tellurium, palladium, cobalt, nickel, iron, phosphor, silicon, rare-earth elements, alkali metals, and alkali earth metals.    Patent Literature 1: Japanese Patent Laid-Open No. 2007-308423    Patent Literature 2: International Publication WO 2009-048553    Patent Literature 3: Japanese Patent Laid-Open No. 10-28862
According to the examination by the present inventors, however, in the case where a molybdenum compound is added during the ammoxidation reaction as in the method described in Patent Document 1, the performance of the catalyst can be restored to nearly an initial state, but cannot be improved so as to exceed the initial state. Accordingly, the ability of the catalyst is still insufficient.
Moreover, in a method described in Patent Document 2, although the problems are not clear because the document and Examples have no sufficient description of the amount to be added of a tungsten compound, excessive addition of a tungsten compound promotes burning of ammonia in a raw material gas to increase the amount of ammonia to be consumed and to decrease the yield of acrylonitrile.
Further, in a method described in Patent Document 3, a facility for impregnating a solution or the like with a catalyst is needed, and the number of steps is increased. Accordingly, cost is increased and the process is complicated.
In view of the above-mentioned situation, an object of the present invention is to provide a method for producing an unsaturated nitrile in which no complicated steps such as impregnation and drying are needed, and a higher selectivity is provided.